It is the present state of art that no basic technique has yet been established to permit conversion of an original into a reproduced picture with good reproducibility in gradation and tone (hereinafter called "picture quality") or with a desired picture quality in the tonal conversion of the original picture for the production of the reproduced picture from the original picture.
In other words, in the production of the reproduced picture with a good or desired picture quality from the original picture, the "non-line drawing conversion technique in the density range of a picture" which may be considered to form a basis for the reproduction is dependent totally on experiences and perception of an operator and is thus non-scientific and non-rational.
The term "non-line drawing conversion technique in the density range of the picture" (hereinafter called the "conversion technique in the density range of the picture" or merely the "tonal conversion technique of the picture") means a technique which is fundamentally different in field from image processing in the spatial range, image processing in the spatial frequency range, image processing of a given picture by a statistical method, and processing techniques for pictorial characteristics of a given picture such as pattern analyses. It rather provides a basic technique for these image processing technology.
Because, it is the crux, basis and fundamental of the tonal conversion of a picture upon production of a reproduced picture that irrespective of the characteristics of the original picture and irrespective of the technical details or means therefor, the picture quality of the original picture be converted at the ratio of 1:1 and the picture quality of the resultant reproduced picture has a suitable density gradient whereby the reproduced picture is felt natural to the visual sensation of man.
However, the present conversion techniques in the density range of a picture (tonal conversion techniques for pictures) are totally dependent on the experiences and perception of man. Moreover, no attempt has been made to improve these techniques to rational and scientific ones. Accordingly, conventional machines, equipment and components for obtaining reproduced pictures on the basis of any of such conventional tonal conversion techniques for pictures as well as conventional systems using in combination two or more of such conventional machines, equipment and components cannot provide reproduced pictures with good reproduction of the picture quality of original pictures. In addition, their constructions are unnecessarily complex and sophisticated, leading to problems in manufacturing costs, ease and convenience in use, repair, maintenance, etc.
These problems can be attributed primarily to the fact that no tonal conversion technique for a picture, which permits scientific and rational reproduction of the picture quality of the original picture at the ratio of 1:1 in a reproduced picture, has yet been established as the above-mentioned basic technique in the conversion technology for pictures.
When consideration is made in actual technique such as reproduction from a color film original as an original a printed picture as a reproduced picture, there is no ideal to rationally grasp the density characteristics raged from the highlight to the shadow of the original picture. Upon production of a printed picture, the continuous tone of an original picture has to be converted into halftone for the printed picture by setting a color-separation characteristic curve or a halftone characteristic curve. The above technique is totally dependent on experiences and perception of the operator.
For the above reason, there exist problems relating to a tonal conversion of a picture, such as a problem relating to the color separation of an original color film with a non-standard quality upon production of a printed picture, a problem relating to soft and hard wares in digital picture processing systems such as a color duplicating machine, which becomes complicated in consequence of expansion of their function, a problem relating to limitation of performance of an exposure light quantity controlling mechanism in printing of a photographic picture, a problem relating to measures counter to sophistication of picture quality control function for a luminous picture such as television pictures, a problem relating to production of binary pictures, halftones, or multivalued pictures with a smooth tone by way of a systematic process in laser printers, ink jet printers, thermal printer, etc., a problem relating to overcoming limitations of photographing time and photographing system in a low illuminance area, a problem relating to simplification of mechanism used in various detection and control apparatus applied picture images, a problem relating to reducing quantity of picture information to be transmitted, a problem relating to simplification of a mechanism in general picture processing systems, improvement of performance of such systems, and reduction of manufacturing cost thereof. These problems arise fundamentally from the fact that the density characteristic of a picture ranged from the highlight area to the shadow area is not rationally grasped and there has not been obtained scientific and rational means or method for correlating an original picture with its reproduced picture. It is therefore totally depending on experiences and perception of man.